/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.extensions.sql;



import com.bff.gaia.unified.sdk.annotations.Experimental;



import java.io.Serializable;



/**

 * Interface to create a UDF in Unified SQL.

 *

 * <p>A static method {@code eval} is required. Here is an example:

 *

 * <blockquote>

 *

 * <pre>

 * public static class MyLeftFunction {

 *   public String eval(

 *       &#64;Parameter(name = "s") String s,

 *       &#64;Parameter(name = "n", optional = true) Integer n) {

 *     return s.substring(0, n == null ? 1 : n);

 *   }

 * }</pre>

 *

 * </blockquote>

 *

 * <p>The first parameter is named "s" and is mandatory, and the second parameter is named "n" and

 * is optional(always NULL if not specified).

 */

@Experimental

public interface UnifiedSqlUdf extends Serializable {

  String UDF_METHOD = "eval";

}